Many contact-start plasma arc torches employ an electrode that is initially biased to a forward position and is subsequently blown to a rearward position by gas pressure as a plasma-sustaining arc is generated. The electrode must be provided electrical power in both the forward and the rearward positions, as well as while moving to the rear position, and the means for providing the power must be structured so as to allow the motion of the electrode. The power-transfer structure may also be required to provide the bias of the electrode toward its forward position and to limit rearward motion of the electrode so as to define its rearward position. One approach to providing such a structure is to employ a spring-loaded plunger that engages the electrode, in combination with means for supplying electrical power to the plunger from a contact element that is electrically connected to a power supply when the torch is assembled. This approach is taught in U.S. Pat. No. 9,227,265.
A particular concern is providing a conductive path to the electrode when it is in its forward position, which has recently been done by passing current through a spring that serves to bias the electrode to its forward position. This approach has been found to create problems of conductivity when the spring is formed from heat-resistant material such as Inconel, which is a poor conductor. To avoid a requirement that the spring conduct current, U.S. Publication 2015/0351213 (incorporated herein by reference) teaches a power transfer assembly that employs conductive elements having mating structures with translating parallel surfaces to provide a conductive path that is independent of the spring. To assure that the surfaces are maintained in contact, the spring employed to bias the electrode is a combination compression and torsion spring that also applies a torsional load to the parallel surfaces to keep them in contact with each other. While this approach has been found effective in providing a conductive path without relying on the spring, it may complicate fabrication of the resulting assembly. Thus, there is a need for a power transfer assembly which can provide the same benefit of providing an independent conductive path to the electrode while simplifying fabrication of the assembly.